doc: Always load Google Analytics script over secure connection

Even if the site is not loaded over HTTPS, it’s good practice to load
assets over HTTPS if that is possible.

Author: paulmenzel

doc/_templates/layout.html

@@ -9,7 +9,7 @@
 
   (function() {
     var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
-    ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
+    ga.src = 'https://ssl.google-analytics.com/ga.js';
     var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
   })();
 </script>